Servo mechanism



May 12, 1936 R. c. RUSSELL SERVO MECHANISM l, 1933 2 Sheets-Sheet 1 Filed Dec.

INVENTOR. Hoke/"- 6T fiasaeZJ.

I BY Wfi%%MQ %M ATTORNEYS.

Patented May 12, 1936 UNITED STATES PATENT OFFICE- SERVO IVIECHANISM Robert 01 Russell, Detroit, Mich.

Application December 1, 1933, Serial No. 700,423

15 Claims.

This invention relates to servo mechanism and particularly to such mechanism as is applicable for use in connection with motor vehicles for enabling operating parts thereof .such, for instance, as the clutch, brake or other devices, to be actuated with a minimum amount of physical eifort on the part of the operator.

Objects of the invention are to provide a servo mechanism that is simple in construction, em-

cient in operation and economical to manufacture; to provide a servo mechanism particularly designed to resist the shock of abnormal return movement of the various parts thereof to normal inoperative position; to provide a servo mechavide a servo mechanism in which the efl'ect of inertia of the moving parts thereof is reduced to a minimum. 4

Other objects are to provide a servo mechanism including a pair of relatively rotatable members adapted for relative longitudinal movement upon relative rotation, one of the members being normally urged for equal rotation with a rotatable part by frictional connection thereto; to provide a servo mechanism including a pair of relatively rotatable and longitudinally movable members one of which is mounted for relative rotation with respect to a rotatable member and is provided with associated resilient means constantly urging it into frictional association with the rotatable part so as to rotate therewith; to provide a servo mechanism including a pair of relatively rotatable members adapted to be moved longitudinally with respect to each other upon relative rotation, one of the members being nornially urged into frictional engagement with the rotatable part for equal rotation therewith and the other of said members having a frictional means associated therewith normally out of engagement therewith but engageable therewith to 40 eifect operation of the servo mechanism; to provide a servo mechanism including inner and outer sleeves and associated interposed bearing members adapted to cause relative longitudinal displacement of one with respect to the other upon relative rotation therebetween, one of the sleeves being mounted upon a relatively rotatable member and resiliently urged toward a predetermined axial position with respect thereto, together with frictional means associated with the other of said sleeves whereby to enable relative rotation to be effected between the two' sleeves; to provide a servo mechanism including a pair of relatively rotatable and longitudinally movable members, both of which are rotatably mounted; and to nism that will not jam in operation; and to pro-' provide a servo mechanism which includes a pair of relatively rotatable and longitudinally movable members, one of which is normally urged to a predetermined axial position under. the influence of resilient means but is longitudinally mov- 6 able in opposition tosuch resilient means under the influence of abnormal forces to which the servo mechanism may be subjected.

Further objects are to provide a clutch and associated servo mechanism of novel construc- 10 tion; to provide a novel combination of a clutch and a servo mechanism; and to provide a clutch and associated servo mechanism in which relative movement may occur between parts of the servo mechanism without causing the servo l5 mechanism to function in .a clutch operative sense.

The above being among the objects of the present invention, the same consists in certain novel features of construction and combination of parts 20 to be hereinafter described with reference to the accompanying drawings, and then claimed, having the above and other objects in view.

In the accompanying drawings which illustrate suitable embodiments of the present invention and in which like numerals refer to like parts throughout the several different views:

Fig. 1 is a fragmentary side elevational view of a power plant unit for a motor vehicle including a portion of the engine, the clutch and the transmission thereof.

Fig. 2 is an enlarged, partially broken vertical sectional view taken axially through the clutch indicated in Fig; 1 and showing the clutch in engaged position and as being provided with a servo mechanism constructed in accordance with the present invention.

Fig. 3 is a fragment of a view similar to that in Fig. 2 but illustrating the position of the clutch and servo mechanism when the clutch is in disengaged position.

Fig. 4 is afragment of a view similar to that illustrated in Figs. 2 and 3 and illustrating the positions which parts of the servo mechanism may assume under abnormal conditions. Fig. 5 is a sectional view taken on the line 55 of Fig. 2.

Fig. 6 is a sectional view taken on the line 6-4 of Fig. 2.

Fig. 7 is a sectional view taken on the line 1-1 of Fig. 2.

Fig. 8 is a fragment of a view similar to that in Figs. 2, 3 and 4 and illustrating a modification in. the form of the servo clutch actuating mechanism. 55

While the servo mechanism forming the subject-matter of the present invention is adaptable for use in connection with a relatively large number of devices, it is particularly adapted for use in connection with the clutch or brakes of a motor vehicle and, accordingly, as a means for illus trating one of its applications it is shown in the accompanying drawings as adapted to operate the clutch of a motor vehicle. The particular mechanism herein shown and described is an improvement on the construction shown and described in my Letters Patent of the United States No. 1,967,563 on Improvements in clutches, granted July 24, 1934.

The main elements of the illustrative embodiment of the present invention herein shown are similar to the same elements shown and described in one modification of my patent above referred to and, while it is to be understood that the construction shown and described in my patent above referred to operates in a satisfactory and acceptable mannenI have found that under certain abnormal conditions of operation difilculties may arise in the operation of the structure there disclosed which difficulties are eliminated by the mechanism provided in accordance with the present invention. I have found that in the structure disclosed in my patent above referred to, where the servo mechanism is applied to clutches of un- :usually high capacity, if the operator of the clutch allows his foot to slip off the control pedal while the clutch is in fully disengaged position, the extremely high pressure of the clutch springs will act so suddenly and forcefully on the servo mechanism as to return the outer member of the servo mechanism toward normal inoperative position with such great speed that the shock of stopping this member subjects the mechanism to excessive strain, and in some cases is liable to cause it to become jammed. An equivalent condition may occur where the servo mechanism is applied to operate any other device actuated in one direction by spring pressure. While such occurrences are comparatively rare and may not cause any damage in any case, there is the possibility that such damage may arise and, accordingly, by the practice of the present invention any possibility thereof is eliminated entirely.

Referring now to the accompanying drawings, there is indicated in Fig. 1 a fragment of the usual type of unitary power plant provided for motor vehicles and which includes an engine l2 having secured to its rear end a clutch housing l4 enclosing a suitable clutch mechanism and in turn to the rear end of which is secured the usual transmission or change speed gearing unit I6.

The particular type of clutch employed within the casing l4 to transmit power from the engine l2 to the transmission unit 16 is immaterial as far as the present invention is concerned, the particular clutch shown by way of illustration being of a conventional spring packed single dry disc type of the following construction. Referring now particularly to Fig. 2, it will be noted that the rear end of the crank shaft for the engine i2 is provided with a radial flange l8 upon which is mounted and to which is secured by means of bolts 26 the usual engine fiy wheel 22 the rim 24 of which projects rearwardly beyond the web 26 thereof. The rear face of the fly wheel web 26 is formed to provide a smooth annular radially extending face 28 against which the clutch driven disc indicated generally at 30 is adapted to be clamped when the clutch is in en- 44 provided in the crank shaft.

gaged position. To the rear face of the rim 24 of the fly wheel 22 is secured by screws 32 a clutch cover 34 and positioned between the cover 34 and the driven disc 30 is the usual pressure plate 36 which is constantly urged toward a position to clamp the driven disc 30 against the face 28 by means of a plurality of coil springs 38 maintained under compression between the cover 34 and the pressure plate 36. I

The clutch shaft 46 which is provided in axial extension of the engine crank shaft is provided with a reduced forward end 42 which is suitably guided and has bearing in the bearing bushing Immediately rearwardly of the reduced end 42 the outer surface of the shaft 46 is splined as at 46 for slidable but relatively non-rotatable engagement with the hub 48 of the clutch driven disc 30. The rear end of the shaft 40 is suitably guided and has bearing in the collar 50 formed on-a-member 52 suitably fixed in the rear end of the clutch housing l4.

The pressure plate 36 is provided with a plurality of equally angularly spaced rearwardly ex1 tending pairs of lugs 64 on its rear face adjacent its outer edge, and slidably received between the radially outer edges of each pair of the lugs 64 is a guiding member 66. The members 66 guide the pressure plate 36 for, movement axially of the shaft 40 with respect to the flywheel 22 but maintain it against relative rotation with respect to the fly wheel 22. Each of the guiding members 66 is provided with an integral stud 68 which projects radially outwardly therefrom through the clutch cover 34. and on the outer side thereof is provided with a nut 10 to lock it in place. Inwardly of the members 66 each pair of the lugs 64 is provided with a pin 12 projecting transversely therethrough which is received in cooperating slots 14 formed in the outer ends of corresponding clutch throwout arms of fingers 16 which project into the space between corresponding pairs of lugs 64 and which extend in a generally radially inwardly direction therefrom throughopenings 18 in the clutch cover 34. Each of the arms 16 is pivotally supported from the clutch cover.34 by means of a post member projecting forwardly through the rear face of the clutch cover 34 and having its forward end bifurcated for reception of the corresponding finger 16 which is pivotally secured thereto by means of a pin 82. The axial position of each of the post members 80 is controlled by a nut 84 threaded thereonto and engaging the rear face of the clutch cover 34, and a coil spring 86 maintained under compression between the forward face of the clutch cover 34 and a suitable shoulder formed on the post member 80.

As will be obvious to those skilled in the art, if the radially inner ends of the clutch fingers 16 are urged forwardly under a sufficient pressure, the fingers 16 will be caused to pivotabout their pivot pins 82 and their outer ends in moving rearwardly will draw the pressure plate 36 therewith against the force of the springs 38 and thereupon will free the clutch driven disc 30 from clamping relation with respect to the flywheel 22. This relation of parts is indicated in Fig. 3. The mechanism thus far described is conventional and forms no part of the present invention and is indicative only of one form of a clutch mechanism to which the'present invention may be satisfactorily applied.

The clutch cover 34 in the present instance shown as being provided with an inward extension 34' which extends in a generally radially inwardly direction to' a point adjacent the outer surface of the rear end of the hub 48 where it has fixed thereto a rearwardly extending sleeve 88 concentric with the shaft 48. For the purpose of fixing the sleeve 88 with respect to the cover portion 34' the sleeve 88 may be provided at its forward end with a radial flange 88 secured to the cover portion 34' by means of rivets 82 or other suitable means. The rear end of the sleeve 88 is provided with an outwardly projecting peripheral bead 94 the forward face of which tapers outwardly and rearwardly as indicated.'

In the'particular instance shown the head 94 is in the form of a split ring which is snapped into a circumferential recess in the sleeve 88.

- Adjacent and surrounding the forward end of the sleeve 88 is a spring member best illustrated in Fig. 5 and shown as including a fiat annular portion 98 provided internally thereof with a plurality of concentric arcuate shaped spring fingers 88 attached to the portion 98 at one end only thereof and the free ends of which are bent rearwardly out of the plane of the portion 98. The fiat portion 88 of this spring member is adapted to lie in contact with the rear face of the cover extension 84 at the inner margin thereof with the fingers 88 extending in a rearwardly direction and in close proximity to the outer surface of the sleeve 88.

A sleeve-like member I88 is rotatably mounted upon the sleeve 88 between the rear ends of the fingers 88 and the bead 84. The rear edge of the member I88 is beveled for complementary engagement with the outwardly and rearwardly tapered face of the head 84 and the length of the member I88 is such that when its rear edge contacts with the bead 94 the spring fingers 98 are maintained under a compressive stress. Thus the spring fingers 88 constantly urge the member I88 rearwardly into engagement with the bead 94 and thereby frictionaily-urge it for equal rotation with the sleeve 88 and consequently the fly wheel 22 or clutch driving member. The tapered conformation of the inter-engaging faces of the bead 94 and member I88 serve to increase the frictional engagement between these parts. The bead 94 therefore not only serves as a stop for limiting rearward travel of the member I88 but additionally serves to frictionally urge it toward equal rotation with the clutch driving member.

Surrounding the sleeve-like member I88 is concentric and slightly spaced relation with respect thereto is a second sleeve-like member I82. The adjacent faces of the members I88 and I82 are provided with opposed thread-like grooves or races I84 and I88 respectively of semi-circular section between which a plurality of ball bearings I88 are received and which not only serve to maintain these members I88 and I82 in concentric relation with respect to each other but also to lock them together for threadedengagement with each other. A relatively thin tubular sleeve II8 received between the opposed faces of the members I88 and I82 is provided with suitable apertures therein for reception of the balls I 88 thereby to maintain them in equally angular spaced relation as best illustrated in Fig. 6. This arrangement of parts, as will be observed, provides a structure wherein relative rotation between the members I88 and I82 will effect relative axial displacement of one with respect to the other.

In order to prevent the ball bearing retainer sleeve II8 from becoming materially displaced from its desired normal position, the inner member I88 is provided with a radial abutment II2 adjacent its rear edge which intersects the possible rearward path of travel of the retainer sleeve H8 to thereby limits its movement in a rearward direction by contact therewith. In the particular instance shown the abutment H2 is illustrated as a split ring which is sprung into a complementary peripheral groove formed in the outer surface of the member I88. In order to limit forward movement of the retainer sleeve H8, a radially outwardly extending lug H4 is struck outwardly from the material of the sleeve Ill adjacent the rear end thereof, this lug I I4 being adapted to contact with the notched rear edge of the outer member I82 in order to limit relative forward movement of the, sleeve II8 with respect thereto.

The outer member I82 is provided with a radially outwardly extending flange H8 adjacent its rear end to which a radially disposed disc H8 is fixed by rivets I28. A disc I22 rotatably surrouhds the outer sleeve member I82 in forwardly spaced relation with respect to the disc I I8 and is separated therefrom by a plurality of ball bearings I24. The ball bearings I24 are maintained in equally angularly spaced relation and maintained against displacement from their intended location by means of a retainer disc I28 rotatably surrounding the member I82 between the discs Il8 and I22 and provided with apertures for receiving the ball bearings I24 therein. As indicated in Figs. 2, 3 and 4, the

disc I22 is positioned for engagement with the inner ends of the clutch fingers I8 so that when the disc I22 is moved forward or to the left as viewed in the drawings, along the shaft 48, the

inner ends of the fingers 18 will be moved forwardly therewith and will cause the pressure plate 38 to be withdrawn from clamping engagement with the clutch driven disc 38 and thereby place the clutch in disengaged position.

Fixed upon the sleeve 58 supporting the rear end of the shaft 48 is a member I28 having a cylindrical outer surface. A sleeve member I88 is slidably mounted upon of the member I28 and is held against rotation with respect thereto by means of a pin I32 threaded into the member I28 and projecting outwardly through a longitudinally extending slot I34 in the sleeve I38. The forward end of the sleeve I38 is formed to provide a radially extending annular flange or plate I38 which, upon forward movement of the sleeve I38, is adapted for interengagement with the disc II8. A ring I38 of friction material is preferably pro vided either uponthe disc H8 or plate I38 to enhance the frictional characteristics of the engagement of these members, this ring I38 in the present case being shown as attached to the disc II8.

Axial movement of the sleeve I38 together with the plate I38 is controlled through a clutch pedal I48 in the same manner as a conventional clutch is controlled. In other words, the pedal I48 is pivotally mounted as at housing I4 or upon the frame of the vehicle and is connected by a link I44 and arm I48 with a shaft I48 extending transversely through the housing I4. Within the housing I4 the shaft I48 has secured thereto the usual clutch throwout yoke I58 the free ends of the arms of which engage abutments I52 formed on diametrically opposite sides of the sleeve I38. Accordingly,

the exterior surf ace I42 either on the clutch when the clutch pedal I40 is depressed the free ends of the clutch throw-out yoke I50 are moved forwardly and through the abutments I52 urge the sleeve I30 and plate I36 forwardly so as to bring the plate I36 into frictional engagement with the ring I38 secured to the disc H8. The throw-out yoke I50 is normally urged toward inoperative position by springs or other suitable means, the particular means shown by way of illustration including a coil spring I54 which, as indicated in Fig. 1, is maintained under tension between an extension on the pedal I40 below its point of pivot and some suitably fixed point such as the power plant. The outer sleeve member I02 with the parts secured thereto or supported thereby is returned from clutch disengaged toward clutch engaged position by the pressure of the springs 38 acting through the inner ends of the clutch fingers I6.

It will be understood that when the clutch structure above described is in engaged position and rotating, the sleeve members I00 and I02 together with the disc I I8 rotate equally with the fiy wheel 22 which, of course, is the clutch driving member. The disc I22 will rotate with the sleeve I02 when the clutch is engaged, the disc I22 and ball bearings I24 serving as a thrust bearing between the disc II8 and the inner ends of the clutch fingers I6 so as to enable pressure to be applied thereto without anyrubbing action between the fingers I6 and the disc II8.

In the operation of the above device, assuming the parts to be in the relative positions indicated in Figs. 1 and 2 and rotating, if the pedal I40 is depressed against the force of the spring I54 the collar I30 with its plate I36 will be moved forwardly, or to the left as viewed in the drawings, until its forward face contacts with the ring I38 secured to the disc II8. When this occurs the frictional engagement between the plate I36 and the disc I38 will tend to retard rotation of the sleeve member I02 with respect to the sleeve member I00, and as soon as this occurs, because of the screw-like association of. these members, the sleeve I02 will be urged forwardly so as to force the disc I22 against the inner ends of the clutch fingers I6. If the depressing movement of the pedal I40 is continued so as to cause the plate I 36 to follow up the forward displacement of the ring I38 and discIIB, the sleeve member I02 will be caused to continue its forward movement until theclutchfingers I6 have moved toward or to the position indicated in Fig. 3 at which time the pressure plate 36 has been withdrawn from clamping engagement with the driven disc 30 and thus placed the clutch in' disengaged position wherein the driving and driven elements of the clutch are free to rotate independently of each other. It might be noted that although the inner sleeve member rotatable upon the sleeve 88 it will ordinarily continue to rotate in direct accordance with the sleeve 88 during disengagement of the clutch for the reason that as soon as any pressure is exerted between the member I02 and the clutch fingers 16 such pressure will act to force the sleeve member I00 rearwardly and to build up the frictional engagement between it and the teeve 88 through engagement of the tapered surfaces at the rear ends of these sleeves. Accordingly, the greater the pressure exerted on the fingers I6 the greater frictional resistance will be set up between the sleeves 88 and I00 to maintain them against relative rotation with to each other.

I00 is respect It might appear at first glance that if the operator suddenly advances the member I36 to throw out the clutch, the member I I8 and sleeve I02 might be moved forwardly before the sleeve I02 has a chance to rotate on the sleeve I00, thus separating the tapered rear end of the sleeve I00 from the abutment 94 and rendering the servo mechanism inoperative for its intended purpose. Such forward movement under such conditions will occur only if the driving member or flywheel is not rotating, and under such conditions will permit manual disengagement of the clutch which is desirable in such cases, but if the driving member is rotating the inertia of the revolving parts,

even in the absence of the spring member 96-98,

I 36 is preferably limited so as to eliminate any possibility of any manual pressure being applied to force the plate I36 forwardly at such time that the inner ends of the clutch fingers I6 may have reached the forward possible limit of their travel,-

for otherwise excessive friction would be set up between the plate I 36 and the friction ring I38 which would set up undue heating of these parts due to the slipping between them and consequently might result in the destruction of these parts. One meansof eliminating this possibility is indicated in the drawings as including a stop screw I56 threaded into a lug I58 projecting outwardly from the sleeve I30 and in a position to engage the pin I32'fixed to the member I28. The screw I56 is adjustable into the lug I58 and may be locked in adjusted position by means of a lock nut I60. As indicated in Fig. 3, when the sleeve I30 has moved far enough forwardly to bring the screw I56 into contact with the pin I 32, the'inner ends of the clutch fingers I6 are still short of the limit of their forward possible movement defined by the margins of the corresponding openings I8 in the clutch cover extension 34'.

A feature of this servo mechanism which enables absolute control over the movement of the mechanism which it is actuating in accordance with the position of the control lever, and whether the servo mechanism is applied to a clutch, brake or other device, will be apparent from the following explanation in connection with the clutch structure shown. It will be observed that when the clutch pedal I40 is depressed to move the plate I36 forwardly and the plate I36 is brought into frictional engagement with the ring I38 on the disc I I8 so as to cause relative rotation thereof, should the movement of the pedal I40 be stopped at this point the disc II8 will move forward only to such extent as the pressure acting on its through the clutch fingers I6 tending to force it rearwardly balances the frictional drag exerted between the plate I36 and ring I38 multiplied by the mechanical advantage of the threadlike engagement between the sleeves I00 and I02. Because of the mechanical advantage of the thread-like engagement of the members I00 and I02 the amount of friction usually set up between the plate I36 and ring I38 will be unusually low and not sufiicient to set up undue heating of the rubbing surfaces thereof even during continuation of such rubbing contact. Should the clutch pedal I 40 now be further depressed, the frictional engagement between the plate I36 and ring I38 will be increased causing a further relative rotation of the disc H8 and outer sleeve member I02 with respect to the inner sleeve. member I00 and the disc H8 and sleeve member I02 will be caused to move further forwardly until the balanced condition above described will have again become established. In other words, it will be apparent that in order to cause complete disengagement of the main clutch, the pedal I40 must be depressed so as to cause the plate I36 to follow up the forward movement of the ring I 38 and disc II8 as these parts move forwardly against the pressure exerted upon them b the clutch fingers 16, until the clutch has been oved to disengaged position. Likewise and for the same reason, the return movement of the mechanism toward clutch engaged position may be just as accurately and progressively controlled as the movement thereof toward clutch disengaged position. Accordingly, engaging and disengaging movements of the clutch may be controlled Just as accurately through the servo mechanism herein provided as they could were the servo mechanism not provided and these movements of the clutch controlled entirely by directly applied manual pressure as in conventional -constructions, the only difference being in this respect that by the use of this servo mechanism only a small percentage of the manual effort required to operate the clutch is required as compared to the pressure necessary where directly manually controlled.

Should the plate I 36 be allowedto return to normal inoperative position at a rate of speed faster than that which the disc H8 and outer sleeve member I02 is capable of equaling, such as may occur where the operator of the clutch is.

holding the clutch in disengaged position and per mits his foot to slip off of the clutch pedal, because of the free rolling engagement between the sleeve members I00 and I02, the rate of rotation of the sleeve member I02 and disc II8 by the time the ring I 38 has moved back into contact with the plate I36, will have set up so much inertia in the moving parts, namely, the member I02, the disc H8 and ring I38, that unless otherwise provided for the overcoming. of this inertia in the, short time necessarily provided might cause damage to the parts involved. This, of course, is more or less an abnormal condition but it is deemed best to guard against it and the servo mechanism herein provided acts to materially reduce the possible ill effect thereof.

Under such circumstances and considering now that the outer sleeve member, together with the disc H8 and ring I38, are being revolved rapidly under pressure from the clutch fingers I6 in an attempt to equal the return speed of the plate I36 which, as is being considered has been returned to the position indicated in Figs. 2 and 4 at a rate of speed faster than can be accomplished by the outer sleeve member I02 and disc II8, the disc II8 will in moving rearwardly due to such rotation, finally bring the ring I38 into contact with the plate I36 while rotating at this relatively high speed. Due to the inertia'of these rotating parts and to the mechanical advantage through which this inertia works by reason of the thread-like engagement between the sleeve members I00 and I02, a relatively great pressure will tend to be set up between the plate I36 and the ring I38. When this contact between the plate I36 and ring I38 occurs the ring I38, together with the disc H8 and outer sleeve member I02, is of course stopped against further rearward movement, but will have a tendency'to continue to rotate, and with the construction provided will rotate a limited amount due to the fact that in continuing to rotate the pressure exerted between the plate I36 and I38 will be now utilized'to force the inner sleeve I00 forwardly against the pressure of the spring fingers 5 98 and this will cause, as illustrated in Fig. 4, the inner sleeve I00 to actually move forwardly away from the bead 84. This provides a material time element in which to absorb the inertia of the rotating parts mentioned,-which time element was lacking in the construction shown and described in my previously filed application above referred to, and thereby reduces the effects thereof to such an extent as to render them of little moment. It may be observed that as the inner sleeve I00 is forced forwardly it is moved out of frictional engagement with the bead 84 on the rear end of the sleeve 88, and under such circumstances the inner sleeve member I00 may actually rotate on the sleeve to increase the 20 aforesaid time element. As soon as the inertia of these rotating parts has been absorbed by the mechanism as explained, the inner sleeve I00 will have been moved re'arwardly by the spring fingers 98 again to normal position as indicatedin Figs. 25 2 and 3 and all of the parts in general will have returned to their normal inoperative positions.

It will, of course, be obvious that the interengageable surfaces of the plate I36 and disc II8 need not be of the disc type illustrated-in Figs. 1 to '7 inclusive in order to obtain the advantages of the present invention. In fact, where the load to be applied by the servo mechanism is unusually high or the space forthe-clutch elements of the servo mechanism itself is restricted, a conical form of clutch such as that illustrated in Fig. 8 may be employed. Referring to Fig. 8 in which parts equivalent to the previously described parts are indicated by the same numerals except that they bear a prime mark, it will be noted that instead of making the member 8' in the form of a full disc the outer marginal portion thereof has been bent rearwardly as at I10 so as to provide a frusto-conical inner surface. The portion I36 of the collar I30 is 5 formed complementarily to the inner surface of the portion I10 and its complementary face is provided with a friction facing I38 adapted for direct contact with the inner face of the portion "0. The operation is, of course, identical to that previously described.

Formal changes may be made in the specific embodiment of the invention described without departing from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claims.

What is claimed is: I

1. In a servo mechanism, in combination with a rotatable member, a pair of relatively rotatable, elements rotatably mounted relative to said member, means frictionally urging one of said eiements for equal rotation with said member, resilient means constantly urging said one of said elements. toward a predetermined axial position with respect to said member, and frictional means including a pair of bodily shiftable members one of which is adapted for rotation an'd -axial movement with said other of said elements; said pair of members being cooperable with each' other to urge said other of said elements toward relative 7 rotation with respect to the first mentioned ele-' h. ment, and means for effecting movement of said other of said pair of members in follow-up relation with said one of said pair of members.

2. In a servo mechanism, in combination with 76 tive rotation between them, and friction means cooperable with the last mentioned element for urging it toward relative rotation and therefore axial movement with respect to the first mentioned element, said friction means being arranged in axially follow-up relation with respect to said last mentioned element.

3. In a servo mechanism, in combination with a rotatable member, a sleeve rotatably and axially slidable with respect to said member, means frictionally urging said element toward equal rotation with said member, a second sleeve surrounding the first mentioned sleeve, means interposed between said sleeves causing relative axial displacement between them upon relative rotation between them, and means frictionally associated in axially follow-up relation with the last mentioned sleeve for urging it toward relative rotation with respect to the first mentioned sleeve.

4T'In'a servomechanism, in combination with a rotatable member, a sleeve'rotatably and axially slidably associated with said member, means for frictionally urging said sleeve toward equal rotation with said member, a second sleeve surrounding the first mentioned sleeve, said sleeves having opposed thread-like grooves formed .in their opposed surfaces, bearing elements received between said opposed grooves, and means frictionally cooperable with said second mentioned sleeve for urging it toward relative rotation with respect to the first mentioned sleeve.

5. In a-servo mechanism, in combination witha rotatable member, an element rotatably and slidably associated with said member, an abutment on said member, an end of said element being formed complementary to said abutment for frictional engagement therewith, means constantly urging said element toward said abutment whereby to cause said end to interengage said abutment and frictionally lock it thereto for equal rotation therewith, a second element rotatably mounted on and axially movable with respect to the first mentioned element and 'cooperatively associated with the first mentioned independently of said means to affect relative axial dislacement between them upon relative rotation between them, and friction means cooperable with the last mentioned element for urging it toward relative rotation with respect to the first mentioned element.

6. In a clutch structure, in combination, a driving member, a. driven member, a pressure plate rotatable with said driving member and axially movable with respect thereto, spring means urging said pressure plate toward clutch engaged position to clamp said driven member to said driving member, fingers associated with said pressure plate for moving it in opposition to said spring means, an element adapted to normally rotate with said driving member, a. second element rotatable relative to the first mentioned element and cooperating therewith to be axially displaced relative thereto upon relative rotation between them, said second element cooperable a rotatable member, an element axially slidably with said fingers upon axial displacement in one direction relative to said first mentioned ele-- ment to disengage said clutch, means frictionally associated with said second element to urge said second element toward relative rotation with respect to said first mentioned element, and means limiting movement of said friction means in one direction. to an amount less than the corresponding maximum displacement of said fingers in the same direction.

7. In a clutch structure, in combination, a driving member, a driven member, a pressure plate rotatable with said driving member and axially movable with respect thereto, spring means urging said pressure plate toward clutch engaged position to clamp said driven member to said driving member, fingers associated with said pressure plate for moving it'in opposition to said spring means, an element adapted to normally rotate with but rotatable relative to said driving element and axially movable with respect thereto, a second element rotatable relative to the first mentioned element and cooperating therewith to be axially displaced relative thereto upon relative rotation between them, said second 25 ond element to urge said second element toward relative rotation with respect to said first mentioned element.

8. In a'clutch structure, in combination, a driving member, a driven member, a pressure axially movable with respect thereto, spring means urging said pressure plate toward clutch engaged position to clamp said driven member to said driving member, fingers associated with said pressure plate for moving it in opposition to said spring means, a sleeve fixed for rotation with said driving element, an element rotatably and axially slidably mounted relativeto said sleeve and having frictional engagement therewith, a second element rotatable relative to the first mentioned element and adapted to be moved axially with respect thereto upon said relative rotation, said second element. being associated with said fingers for corresponding movement in at least one direction, and means irictionally engageable with said second element for urging it toward relative rotation with respect to the first mentioned element.

9. In a clutch structure, in combination, a driving member, a driven member, a pressure plate adapted to clamp said driven member to said driving member, and means for releasing said pressure plate from clamping position including a pair of relatively rotatable members, means independent of said pressure plate frictionally urging one of said members for rotation with said driving member, said members having cooperating axially inclined surfaces, anti-fricplate rotatable with-said driving member and tion members interposed between said inclined tively rotatable with respect to the first mentioned member, said members being'so formed and so cooperating with each other that relative rotation between them effects axial advancement of said second member relative to the first mentioned member, means operatively connecting said second member'and said pressure plate for correlated movements, a part axially and rotatably movable with saidsecond member, a second nonrotatable part movable axially oflsaid clutch and arranged for frictional engagement with the first mentioned part, and means for controlling the axial position of said second part.

11. In a clutch structure, in combination, a driving element, a driven element, a pressure plate adapted to clamp said driven element to said driving element, spring means constantly urging said pressure plate toward said clamping position, a member rotatably and axially slidably mounted relative to said driving element, means frictionally urging said member toward equal rotation with said driving element and limiting axial movement of said member in one direction, a second member relatively rotatable with respect to the first mentioned member, anti-friction means interposed between said members, said members being so formed and so cooperating with each other that relative rotation between them effects axial advancement of said second member relative to the first mentioned member, means operatively connecting said second member and said pressure plate for correlated movements, 9. part axially and rotatably movable with said second member, a second non-rotatable part movable axially of said clutch and arranged for Eric-- tional engagement with the first mentioned part, and means for controlling the axial position of said second part.

12. In a clutch structure, in combination, a driving element, a driven element, a pressure plate adapted to clamp said driven element to said driving element, spring means constantly urging said pressure plate toward said clamping position, a member rotatably and axially slidably mounted relative to said driving element, means including resilient means constantly urging said member toward one limit of its axially movable position and stop means limiting said axial movement in one direction for frictionally urging said member toward equal rotation with said driving element, a second member relatively rotatable with respect to the first mentioned member, antifriction means interposed between said members, said members being so formed and so cooperating with each other that relative rotation between them effects axial advancement of said second member relative to the first mentioned member, means operatively connecting said second member and said pressure plate for correlatedmovements, a part axially and rotatably movable with said second member, a second non-rotatable part movable axially of said clutch and arranged for frictional engagement with the first mentioned part, and means for controlling the axial position of said second part.

13. In combination with a rotatable driving part, a driven part adapted for frictional engag'ement therewith, and a part constantly urged in a direction to clamp said driving and driven parts.

together for equal rotation and required to be actuated in an axial direction with respect thereto to release said frictional engagement, a member fixed for rotation with said driving part, an element rotatably mounted on said member, frictional means independent of the third mentioned part constantly urging said element toward equal rotation with said member, a second element rotatably associated with the first mentioned element and so constructed and arranged as to move axially relative to the first mentioned element upon relative rotation with respect thereto, means carried by said second element cooperable with the third mentioned part to effect axial displacement of said third mentioned part upon axial -movement of said second element, and means for causing relative rotation between said elements.

14. In combination with a rotatable driving part and a part to be actuated in an axial direction with respect thereto, a member fixed for rotation with said driving part, an element rotatably mounted on said member, frictional means independent of the second mentioned part constantly urging said element toward equal rotation with said member, a second element rotatably associated with the first mentioned element and so constructed and arranged as to move axially relative to the first mentioned element upon relative rotation with respect thereto, means carried by said second element cooperable with the second mentioned part to effect axial placement of said second mentioned part upon axial movement of said second element, and means arranged in axially follow-up relation with respect to said second element for controlling relative rotation between said elements.

15. In a clutch structure, in combination, a rotatable driving part, a driven part constantly urged toward frictional engagement therewith, means movable axially of said clutch for releasing said frictional engagement and means for moving the first mentioned means including, a. pair of relatively rotatable members so constructed and arranged as to efiect axial movement of one thereof with respect to the other thereof upon relative rotation between them, frictional means tending to maintain the normal position of one of said members but yieldable under abnormal forces present therein to permit shifting of said one of said members, and means under the manual control of the operator of said clutch for utilizing rotation of said driving member to effect relative rotation between said members.

ROBERT C. RUSSELL.

cERT'IrrcATE or CORRECTION.

Patent No. 2,040,409. My 12, 1936.

- ROBERT c. RUSSELL.

It is hereby certified that error appears in theprinted specification of the above numbered patent requiring oorrectionas follows: Page 6, first column, line 55, claim 5, after "mentioned" insert theword elementfand that the said Letters Patent-should be readwith this correction therein that the same may conform to the record of the case in the. Patent Office.

Signed and sealed this 50th day of June, A. D. 1936'.

Henry Van Arsd'als ISeal) i Acting-Commissioner or Patents. 

